Fluorescence is generally understood to be a property that enables certain materials to absorb light energy and radiate visible light at a longer wavelength than the absorbed light. Without being limited to any specific theory, it is widely accepted that electrons in fluorescent materials are excited upon being illuminated by light energy of a specific wavelength, and light energy of a longer wavelength is radiated from these materials as the electrons return to the unexcited or ground state. The specific excitation and radiation wavelengths are characteristics of the particular fluorescent materials. The apparent brightness of a fluorescent material's luminescence is dependent, among other factors, on the wavelength emitted by the material and the intensity of the incident radiation that excites the material. A fluorescent material that has its excitation peak at a specific wavelength may quickly emit a much reduced luminescence as the wavelength of incident light deviates from the excitation peak, and will lose the ability to fluoresce when the incident light does not have enough energy within the specific excitation range.
Lamps emitting radiation that excites fluorescence have been used for a wide variety of purposes, including, but not limited to, forensic inspection, readmission control, counterfeit currency detection, contamination inspection, non-destructive testing, and detecting leaks in air conditioning and other fluid-containing systems. The lamplight is commonly in the ultraviolet (UV) or in the visible blue-violet range, exciting a fluorescence somewhere in the visible range. The fluorescent material may be deliberately provided. For example, some banknotes have a fluorescent marker embedded in the paper and the UV light is used to detect the otherwise hidden marker. In another example, one method for detecting leaks in an air conditioning system is through the use of fluorescent dyes that are added to and mixed with the refrigerant in the system, with the combination of refrigerant and dye circulating through the air conditioning system. This method was first pioneered by Spectronics Corporation, the assignee of the present invention. In these leak detection systems, the dye circulates through the system, eventually seeping out at the source of the leak. When exposed to a suitable light source, such as an ultraviolet (UV) light, the dye fluoresces, thus highlighting the source of the leak. Stamps using an ink that is visible only by fluorescence under an ultraviolet lamp are used as re-admission stamps at entertainment events.
The fluorescence may be an incidental property of some material that it is desired to detect, measure, or observe. For example, many biological materials, including rodent hair and urine, are naturally fluorescent. Other examples of the use of fluorescence include the detection of counterfeit currency and other documents. Many minerals can be recognized or distinguished by their levels and colors of natural fluorescence.
Ultraviolet lamps may also be used to produce an effect on an object, for example, in sterilization, erasing EPROMs, or DNA/RNA cross-linking or otherwise setting or hardening various plastic materials.
Additionally, ultraviolet lamps have been used for germicidal detection and decontamination. One successful example of such a device was developed by Spectronics Corporation, the assignee of the present invention, and is described in U.S. Pat. No. 6,953,940.
The visibility of the fluorescent response is increased when the intensity of other visible light is reduced, so that the fluorescent response is not masked or washed-out by other light. Thus, ultraviolet lamps directed in otherwise dark conditions at a system containing a UV responsive fluorescent material may reveal the fluorescent material glowing against the dark background.
Many current fluorescence-exciting lamps emit light in long wave ultraviolet (UV-A) wavelength range of about 320 nm to about 400 nm, for example, around 365 nm, or in the medium wave ultraviolet (UV-B) range from about 280 nm to about 320 nm, for example, around 315 nm, or in the short wave ultraviolet (UV-C) range, for example, around 254 nm, or in the visible violet/blue range from about 400 nm to about 480 nm within the electromagnetic spectrum.
For many purposes, a battery operated hand-held lamp that can be directed at less-accessible areas is desirable. Existing lamps powered by an external AC or DC power source have a trailing power lead that hinders maneuvering of the lamp, and cannot be used where a suitable power source is not available. Many existing battery powered lamps are heavy and bulky. The size and shape of the lamp typically hinders maneuvering of the lamp, makes the lamp awkward to grasp in the hand, or both. Small lamps do exist, for example, the UV-4B Series battery operated ultraviolet lamps manufactured and sold by Spectronics Corporation are only about 16 cm long by 2.5 cm wide by 5 cm from front to back. Those lamps are deep from front to back, with the actual light source positioned along one narrow side of the lamp unit.
A smaller, hand-held UV lamp was developed by Spectronics Corporation and is described in U.S. Pat. No. 6,953,940, referred to above and which is incorporated herein by reference in its entirety. That lamp is light and easily maneuverable. However, the small area of illumination generated by the lamp makes inspection of larger areas more time consuming. More particularly, the narrow width of the unit permits light from the surrounding environment to sometimes overpower the fluorescent response in brightly lit rooms, thus making detection difficult.
A need, therefore, exists for a battery-powered inspection lamp that is compact, easy to hold, and provides higher output (microwatts/cm2) of the desired wavelength.